https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87544
--- Comment #13 from Martin Sebor <msebor at gcc dot gnu.org> --- There is a call to malloc(SIZE_MAX - 15) in GIMPLE, as a result of the conditional and I believe jump threading. Just after thread1 we see this in the vrp1 dump: <bb 20> [local count: 32272892]: # _91 = PHI <_54(4), _6(6)> # iftmp.2_92 = PHI <1152921504606846975(4), 1152921504606846975(6)> size_94 = iftmp.2_92 * 16; result_96 = __builtin_malloc (size_94); goto <bb 9>; [100.00%] and after cselim: <bb 20> [local count: 32272892]: # _91 = PHI <_54(4), _6(6)> size_94 = 18446744073709551600; result_96 = __builtin_malloc (size_94); goto <bb 9>; [100.00%] which is then propagated into malloc. That's what the warning sees. I think the malloc folding would be fine (provided errno was set as well) but operator new probably wouldn't be because the operator is replaceable so it could be detected (unless the standard was changed to allow the elision).
